1. Field of the Invention
The present invention relates to methods for remotely measuring temperature, and more particularly to a satellite method for measuring sea surface temperature.
2. Description of Prior Art
A major factor limiting the accuracy of satellite infrared measurements of sea surface temperature is the inability to accurately account for the absorption and emission of the intervening atmosphere. The calculation of atmospheric corrections from radiosonde data and force-fitting satellite temperatures to surface data have been two popular methods of making corrections for atmospheric effects. Both methods require the assumption of a horizontally uniform atmosphere since they apply a correction based on observations at one or two points to data over ocean areas many hundreds of kilometers in size. However, horizontal uniformity in the atmosphere often does not exist, especially in areas of high surface temperature gradients. Here, coupling between the atmosphere and the ocean produces atmospheric temperature and water vapor gradients which reflect the sea surface temperature patterns below. Atmospheric corrections which vary spatially to compensate for horizontal atmospheric variability are required for consistently accurate measurements of sea surface temperature.
Several approaches to a spatially variant atmospheric correction have been proposed. One technique uses the High Resolution Infrared Sounder (HIRS) for atmospheric correction. This technique is limited by the fact that HIRS provides relatively crude estimates of temperature and humidity profiles with poor spatial resolution (42 Km along-track sampling interval). The multiple window approach is another spatially variant correction possibility. Present generation satellites with channels at 3.55-3.93 .mu.m, 10.5-11.5 .mu.m and 11.5-12.5 .mu.m offer the potential for atmospheric correction based on differences between observed sea surface temperatures in these three spectral windows. The temperature differences arise from varying degrees of atmospheric water vapor absorption at the different wavelengths. However, due to noise and possible sunlight contamination at 3.55-3.93 .mu.m, and calibration problems, this approach has developed slowly.
Another recent approach to spatially variant atmospheric corrections uses a least-squares polynomial fit to corrections calculated from a set of shore-based radiosondes. This method is limited to regional-scale areas where the atmosphere can be accounted for synoptically. The method further assumes that shore-based radiosonde data adequately represents the marine environment.
Thus, what is desired is a method for achieving spatially variant atmospheric corrections with high accuracy over the marine environment.